Thermoplastic adhesives, especially hot melts, can be confectioned and packaged as disclosed in German patent 22 48 046. Hot melt adhesive is squeeze-cut into roughly pillow-shaped pieces, the pieces are subsequently cooled and thus solidified and are then put into sacks or cartons for packaging.
In order to reduce the tendency of the individual pillows to stick, i.e. adhere to each other, it is known to coat them with a separating, anti-stick substance, such as wax or a polymer, as shown in DE 33 27 289 Kaiser. WO 84/03457 and WO 84/03468, Societe Nouvelle Raffinerie Meridionale de Ceresines-Belix, disclose a method to outwardly coat autoprotected blocks with a powdery separating agent. For thermoplastic adhesive compositions with a relatively high softening point (above 120.degree. C. and especially above 150.degree. C.) these coatings provide sufficient anti-stick properties. Such compositions can therefore be packaged, stored and dispensed from sacks without any major sticking problems.
Another packaging for adhesive compositions is to wrap or cast bigger portions of the adhesive in plastics film material, such as thick polyethylene film. These known packagings have the disadvantage that the thermoplastic adhesive composition must be removed from the packaging prior to use, which means an extra handling step. Further, the packaging material must be discarded after emptying, which leads to material waste and expenditure for disposing of the used packaging material.
German patent 36 25 358 to Hausdorf discloses a method to completely wrap a single solid hot melt adhesive material block in a thermoplastic, especially a copolyamide film material with a melting point between 120.degree. C. and 150.degree. C., to prevent sticking of the adhesive to the internal surfaces of a melting apparatus when pressure-melting the adhesive. The film material is melted and mixed with the adhesive. This prior art centers on copolyamide materials in view of their inherent hot melt adhesive properties. Today, application temperatures of less than 150.degree. C., preferably in the range of 110.degree. C. to 140.degree. C. are required by the end user to reduce thermal degradation problems of the adhesive as well as distortion of the substrates used. Therefore, for most applications, copolyamide films are not advantageous in view of their high melting points and problems encountered in homogeneously melting and mixing such materials together with customary hot melt adhesives.
U.S. Pat. No. 4,337,181 discloses film forming formulations comprising starch based films which can be blown into films and used as biodegradable films.
U.S. Pat. No. 4,503,098 discloses disposable articles made from water soluble polymers. The water soluble polymers include poly (alkylene oxide), hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone polyacrylamide, polyacrylic acid, poly(vinyl methyl ether-co-maleic anhydride) with a degradable water-insoluble polymer selected from cyclic ester polymer, a poly .beta. hydroxy butyrate, a dialkanoyl polymer, or an ethylene polymer.
The modes of biodegradation of plastics was studied in an article entitled Degradable Plastics, Materials Forum (1989) 13, 1-10, M. J. Robey, G. Field and M. Styzinski. Many uses of biodegradable polymers including those in the medical science area were highlighted.
However, to date, there has not been a satisfactory solution proposed for a biodegradable packaging for pillowed adhesives as described above.
There is a need in the industry for a packaging material which exhibits biodegradability. If such a package were available, the packaged hot melt pillows would be opened, the hot melt pillows would be poured into the premelt tank, and the film package could be discarded in the trash receptacle. The spent packages would then be transported to a compost facility. The previous films would often take years to break down into components small enough to be digested by bacteria. Thus, from an environmental standpoint, it is advantageous to have a film which biodegrades as quickly as possible.
It is an object of this invention to provide an adhesive package which is biodegradable. Biodegradability is generally defined as a product which breaks down and is physically and substantially consumed by microorganisms under conditions typically present in waste composting processes.
A further problem encountered with some previous films includes noncompatibility with the packaged adhesive when the bag is incorporated with the molten adhesive. Upon melting of the packaged adhesive, the molten film does not form a substantially homogeneous mixture with the molten adhesive. Thus, when the film does not become assimilated into the adhesive, the film can separate and degrade upon heating and can create problems with the hot melt application equipment. By the term "degrade" it is meant an unassimilated portion of the film gels, chars, or skins upon exposure to heat. The resultant mixture can clog nozzles and guns of hot melt application equipment. Thus, it is an important object of this invention to provide a film which blends into the molten adhesive and does not gel, separate or degrade upon heating of the molten adhesive with the dissolved package.
It is a further object of this invention to limit any change in viscosity of the molten adhesive when the film mixes with the adhesive. It is critical in many applications to have minimal changes in the viscosity, and thus the bag should not adversely effect the viscosity.
To attain these and other objects and advantages, a method of packaging an adhesive composition with a biodegradable film is shown as well as criteria for the selection of the biodegradable films.